EXPRESSION AND FUNCTION OF CD59 ON COLONIC ADENOCARCINOMA CELLS

The expression and function of CD59, a 19-25 kDa membrane glycoprotein that inhibits formation of the membrane attack complex of complement, was analyzed on normal and malignant human colonic epithelial cells. A nalysis by immuno-fluorescence demonstrated a weak apical expression o f CD59 on normal intestinal epithelium, with an increased expression o n adenocarcinoma cells. The expression of CD59 was greatest on tumor c ells with poor differentiation. The functional activity of CD59 on hum an adenocarcinoma cells was investigated using the colonic adenocarcin oma cell line HT29. CD59 on HT29 cells was glycosyl-phosphatidylinosit ol-linked, and had a molecular mass of 19-25 kDa. HT29 cells expressed approximately four times more CD59 than leukocytes, and showed a high resistance to antibody-dependent complement-mediated lysis. Blocking of CD59 with divalent antigen-binding F(ab')(2) fragments of the anti- CD59 monoclonal antibody 1F5 resulted in a dose-dependent increase in complement-mediated lysis, suggesting that CD59 may be of importance i n protecting colonic adenocarcinoma cells against complement-mediated cytolysis.